Erythromycins A through D, represented by formula (E) as illustrated below,
 ErythromycinRaRbA—OH—CH3B—H—CH3C—OH—HD—H—Hare well-known and potent antibacterial agents, used widely to treat and prevent bacterial infection. As with other antibacterials, however, bacterial strains having resistance or insufficient susceptibility to erythromycin have been identified. Also, erythromycin A has only weak activity against Gram-negative bacteria. Therefore, there is a continuing need to identify new erythromycin derivative compounds which possess improved antibacterial activity, which have less potential for developing resistance, which possess the desired Gram-negative activity, or which possess unexpected selectivity against target microorganisms. Consequently, numerous investigators have prepared chemical derivatives of erythromycin in an attempt to obtain analogs having modified or improved profiles of antibiotic activity.
Kashimura et al. have disclosed 6-O-methylerythromycin derivatives having a tricyclic basic nuclear structure in European Application 559896, published Nov. 11, 1991. Also, Asaka et al. have disclosed 5-O-desosminylerythronolide derivatives containing a tricyclic carbamate structure in PCT Application WO 93/21200, published Apr. 22, 1992.
Recently erythromycin derivatives containing a variety of substituents at the 6-O position have been disclosed in U.S. Pat. Nos. 5,866,549, 6,075,011 and 6,420,555 B1 as well as PCT Applications WO 00/78773 and WO 03/024986. Furthermore, Ma et. al. have described erythromycin derivatives with aryl groups tethered to the C-6 position in J. Med Chem., 44, pp 4137–4156 (2001).